Lectins have been used widely as a probe for study of cell surface saccharides although the specificities of lectins is too broad to specify a definite carbohydrate structure on the cell surface. Furthermore, lectins are multivalent, difficult to convert into a monovalent state, they are, therefore, pinocytocyzed rapidly by cells, and express various cytotoxicities. In contrast, the anti-carbohydrate antibody directed against a defined single carbohydrate structure of a glycolipid or oligosaccharide derivative shows narrow specificity, no demonstrable cytotoxicity, and is readily converted to a mono-valent fragment (Fab). This proposal includes: 1) Extensive studies on basic conditions for preparation of and general properties of a large variety of monospecific anti-carbohydrate antibodies, and 2) use of such antibodies and their monovalent derivatives in various cell biological studies: a) determination of the quantity and the quality of various saccharides on cell surfaces and in intracellular membranes as related to animal cell functions (cell contact, cell cycle, cell proliferation, etc.); b) effect of multivalent and monovalent antibodies on surface functons; and c) effect or purified anti-carbohydrate antibodies on lymphocyte-mediated immune reaction such as blocking of target cell destruction. The approach will be useful in solving various problems in cell biology, particularly the control mechanism of cell proliferation through membrane-saccharides.